MTU Workarounds

The maximum transmission unit (MTU) is the largest size frame or packet — in bytes or octets (eight-bit bytes) — that can be transmitted across a data link. It is most used in reference to packet size on an Ethernet network using the Internet Protocol (IP). A deprecated term is “window size”. Default is 1500 which is too big for the remote station network. Symptoms are, the radio shows up in the Smartlink window but a connection attempt times out.

At least two workarounds are possible which will have no effect on any other applications or users on the router. The first one is to change the settings in the main router for the home. Find the settings for MTU in the network configuration and change the MTU to 1438.

The second workaround uses the command line to do network shell routines. This routine can change the MTU on the PC. Open cmd with administrator permissions and enter these commands.

>netsh

>interface

>ipv4

>show int Look for the line that shows the connection to the Internet and write down it’s name. An example is “Ethernet”. Observe the value in the MTU column. Is it 1500?

Enter the following command.

>set subinterface “Ethernet” mtu=1438 store=persistent where “Ethernet” is the name obtained in the previous name.

An “ok” will be returned if these steps worked. To test, enter the following command:

>netsh int ip show int

The results returned will show the current MTU.

Note that the magic number may be lower or higher. Experiment, if the one above doesn’t work.

To return to normal, close the cmd window.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s